Corrugated steel pipe sections can be used to form pipeline drainage systems along or beneath highways, or for various other construction projects where diversion of water flow or drainage of runoff is required. Depending upon the size and nature of the project, the dimensions of the corrugated steel pipe that are used to form the drainage system may vary. Steel corrugated pipe sections of this type range in diameter from 24" to 144", are made in lengths of up to 24', and have a thickness of 0.064"-16 gauge up to 0.168', or 8 gauge. Typical weights for such pipe sections are given in pounds/foot of length. For example, a 144" diameter pipe has a weight of 400 pounds/foot.
Full-round pipe is suitable for most typical applications. However, sometimes it is beneficial to use a pipe arch, which is round pipe that has been forcibly widened at the bottom The low, wide pipearch design redistributes the runoff area horizontally to provide adequate drainage capacity without necessitating a lowering of the grade, as would otherwise be required with a round pipe. In some cases, use of pipe arch can reduce fill work and grading by as much as one-fourth. The pipe-arch design also is valuable where fast, unrestricted runoff is required. It functions more effectively at low water levels than round pipe.
When a section of pipe is arched, the widest horizontal span of the arched pipe becomes greater than the original diameter, while the height is reduced. For example, an arched pipe section which had an original diameter of 144" will have a horizontal span of about 178" at its widest point. Similarly, an arched pipe having an original diameter of 120" will have a horizontal span of about 137". For pipe sections having an original diameter of 120" or greater, the arched section will have a horizontal span which is sufficiently great so as to require that it be designated as a "wide load" when transported via highway routes to the job site. Generally, transportation of a wide load requires accompaniment by leading and trailing escort vehicles, along with other safety precautions, such as notification banners and the like, all of which drive up the cost of shipping.
Prior pipe arches have been formed in the factory, either by an external pipe arching machine or by an internal pipe arching machine. To affect external pipe arching, force is applied directly to the external surface of the pipe to compress it until a desired shape is obtained Such an external pipe arching apparatus is disclosed in U.S. Pat. No. 2,286,197. Although pipe arched by an external pipe arching apparatus is suitable for some applications, a more uniform arch can be obtained by using an internal pipe arching machine.
A typical internal pipe arching apparatus utilizes a cantilevered horizontal beam rigidly secured at a fixed end, with longitudinally extending forming segments mounted upon opposite sides of the beam. The beam is about 25 feet long. The forming segments are extendable in opposite directions in a horizontal plane to forcibly deform the internal side walls of a pipe section that is suspended on the beam. In order to accommodate different sizes of pipe, the forming segments are made in different sizes and are removably mounted to the opposite sides of the horizontal beam. During arching, the pipe section is suspended in order to allow the top and bottom surfaces to flatten as the sides are elongated. The horizontal beam is mounted a sufficient distance above the floor to enable various sizes of pipe to be moved over the beam prior to arching, and withdrawn from the beam after arching. This movement must be performed via an overhead crane, or some other type of lifting device.
The beam and the mounted forming segments have a total weight of about 40,000 pounds. Additionally, a pipe section on the machine may have a weight of as much as 400 lbs/ft at lengths of up to 24 feet. Due to the cumulative effect of supporting this combined weight over a period of time, at a fixed end of the beam, the horizontal beam will eventually bow in a downward direction. Because the forming segments are mounted longitudinally alongside the beam, downward bowing of the beam affects the path of extension of the forming segments during arching, thus resulting in a pipe that is not uniformly arched along its length. After a certain amount of bowing, the beam cannot be used anymore.
In the past, to minimize the effects of bowing, the horizontal beam has been be bowed slightly upwardly during manufacture, thereby compensating for some of the bending that will eventually occur. However, this is only a temporary solution, and an unsuitable one at that. Depending upon the height of the horizontal beam above the floor, and the diameter of the pipe to be arched, it is sometimes necessary to also raise the horizontal beam and forming segments with respect to the floor in order to suspend the pipe in the air. Thus, the fixed end of the horizontal beam must not only be able to support the total weight of the structure, it also must be mounted for vertical movement.
To reduce the combined moment of inertia that is created at the fixed end of the beam during vertical raising, a hydraulic jack can be attached at the free end of the beam to provide additional, liftable support, enabling the beam to be lifted at both ends. However, the jack must be disconnected from the beam in order to move a section of pipe over the free end of the beam before arching and reconnected once the pipe section is in place, thus requiring additional steps in order to affect pipe arching. Moreover, although the useful life of the beam may be extended somewhat by providing support at both ends, it is still required that the fixed end of the beam be able to support the total weight of the beam, the forming segments and the suspended pipe during those times when the jack is not connected.
The following is a list of patents as background to this invention, and no representation is made that they are pertinent or relevant prior art: U.S. Pat. Nos. 2,474,887; 2,846,102; 2,916,076; 3,392,858; 3,747,394; 3,996,783; 4,004,444; 4,005,793; 4,270,379; 4,279,567; and 4,289,442.